The gem cutter is an object available in The Sims 3: Supernatural. This object allows a Sim to process gems manually, instead of paying the crafter to make the cut. A Sim may craft a bundle of gems of the same kind at once, instead of doing it one by one. By default, the Emerald cut is available, and this item also allows the Sim to grind the gem into dust, assisting the Sim in gathering materials to use in Alchemy. The Sim may process the gem in any ways the Sim has unlocked.
Using the cutter to convert the gem into dust is not financially advisable, as a Sim will get 2-3 piles of dust, each with a price less than a third of the value of the original gem. However, since dust counts as a valid Alchemy ingredient whenever a recipe calls for a gem, it is a very sound choice if you aim to use the gem for Alchemy.
Although producing dust is one of the main purposes of the gem cutter, it also carries other benefits: a Sim can now process the gem as they please without having to wait a day for the mail. Additionally, the gem cutter has no operating cost outside the initial input of cash (and the gem), and it will reliably produce gem dust (usually one or two units, although some say one could get 6 dust per gem) alongside the main processed gem. Given that it is relatively cheap at §975, it is a useful investment for gem collectors. With that said, the gem cutter's synergy with Tiberium is difficult to overstate, as the dust may also turn into the large spire cut that makes Tiberium so valuable. However, Tiberium cannot be processed into dust directly.
Despite the versatility (and profitability) of the gem cutter, it has its drawbacks. Foremost being the fact that it generates noise that wakes everyone around the house (asides from those with the Heavy Sleeper trait). It also causes nearby Sims to spawn a thought bubble indicating their disdain for the gem cutter, although there is not a wish (yet to be discovered) available to Sims to have the gem cutter sold.